1. Technical Field of the Invention
The present invention relates to a semiconductor device employing copper interconnects therein, and more particularly to a semiconductor device employing aluminum as bonding pads in addition to the copper interconnects to improve reliability of semiconductor device, and further a method for manufacturing the same.
2. Description of the Related Art
Generally, copper exhibits low resistance and provides high resistance against electromigration, and therefore, it becomes apparent that copper is the material of choice for interconnect lines and contacts in future generations including the subquarter-micron generation. At the same time, copper is essentially a material that is quite easily oxidized and easily enhances its oxidation due to moisture in air, and once when copper begins oxidation, the copper allows the oxidation to deeply progress into the inside of the copper without staying the surface layer thereof. For this reason, when a bonding pad is formed of a part of copper interconnects and an oxide layer is formed on a surface of the bonding pad, a bonding ball cannot be bonded to the bonding pad with sufficient adhesion strength. In addition, even when the bonding ball could successfully be bonded thereto, corrosion due to oxidation of copper would start from an exposed portion of the bonding pad, which portion is not covered by the bonding ball, and finally spread over the entire surface of the bonding pad. When formation of the corrosion is further enhanced, copper interconnects themselves are unfavorably corroded.
Accordingly, when copper is employed as an interconnects material, a bonding pad made of a material excluding copper and providing high resistance against oxidation is formed on an upper portion of copper interconnects, which technique is generally employed in this technical field. For example, Japanese Patent Application Laid-open No. 7(1995)-201909 discloses a technique in which a tungsten film is laminated on copper interconnects to form a bonding pad. Furthermore, Japanese Patent Application Laid-open No. 10(1998)-340920 discloses a technique in which a conductive film containing aluminum therein is laminated on copper interconnects to form a bonding pad. That is, in both the techniques disclosed in the above-stated publications, copper interconnects are covered by an insulation film and openings are formed in the insulation film to expose a part of the copper interconnects, and then, a conductive film made of tungsten, aluminum or the like is formed within each of the openings on the copper interconnects to thereby form a bonding pad.
However, according to the techniques disclosed in those publications, when a thickness of the insulation film covering the copper interconnects is made large, a film thickness of tungsten, aluminum or the like constituting the bonding pad becomes large, likely presenting performance and manufacturing problems. In particular, an insulation film consisting of a laminated structure having a copper diffusion barrier layer for preventing diffusion of copper and an insulation film is formed into a thick film, presenting a serious problem. For example, FIGS. 1A through 1E each illustrate a cross sectional view of an example in the order of manufacturing steps and the example is constructed by forming a bonding pad made of aluminum on copper interconnects.
Referring to FIG. 1A, a silicon oxide film 201 is formed on a surface of a semiconductor substrate (not shown) having elements such as transistors formed in a surface portion thereof and a trench 202 for an interconnect pattern is formed in the silicon oxide film 201, and then, a barrier metal 203 is formed on an entire surface of a semiconductor device to fill the trench 202 with the barrier metal to prevent copper from diffusing into the oxide, and further, a copper film is formed thereon by a plating method or the like. Subsequently, the copper film on the silicon oxide film 201 is polished such as by a CMP (Chemical Mechanical Polishing) method to leave the copper film only within the trench 202 to thereby form a copper pad 205 that constitutes one piece structure together with copper interconnects (not shown).
Thereafter, as shown in FIG. 1B, a copper diffusion barrier layer 206 made of a silicon nitride film or the like and a silicon oxide film 207 are laminated to cover a surface of the above-stated copper pad 205 to thereby form an inter layer insulation film 208. Then, an opening 209 is formed in the inter layer insulation film 208 to expose a part of the copper pad 205.
Subsequently, as shown in FIG. 1C, a titanium nitride film 212 for preventing reaction between copper and aluminum, an aluminum film 213 and a titanium nitride film 214 for reducing reflectance of a surface of aluminum to make possible the application of photolithography technology in forming a fine interconnect pattern are formed in order.
Then, as shown in FIG. 1D, the titanium nitride film 214, aluminum film 213 and titanium nitride film 212 are etched using a photolithography technique to thereby form an aluminum pad 213 made of the aluminum film 213.
Furthermore, as shown in FIG. 1E, an insulating protection film 215 made of a silicon oxide film or the like is deposited on an entire surface of the semiconductor substrate. Thereafter, the insulating protection film 215 and the titanium nitride film 214 on the aluminum pad 213 are selectively etched and removed using a photolithography technique to expose a surface of the aluminum film 213 to thereby complete formation of bonding pad.
The conventional bonding pad constructed by forming the inter layer insulation film 208 consisting of a laminated structure having the copper diffusion barrier layer 206 for preventing copper diffusion from the copper pad 205 and the silicon oxide film 207, and the insulating protection film 215 positioned on the inter layer insulation film includes the following problem. That is, since the inter layer insulation film 208 is formed on the copper pad 205 to resultantly have a large film thickness owing to its laminated structure and the aluminum pad 213 is formed so as to cover the opening 209 that is formed in the inter layer insulation film 208, the aluminum pad 213 is forced to have a large step, which is formed by the opening 209, and therefore, the step coverage of the aluminum pad 213 at the opening 209 is deteriorated, whereby the copper pad 205 under the aluminum pad 213 suffers from corrosion and/or oxidation due to leakage of moisture and/or oxygen through a portion corresponding to nonconformal step coverage of the aluminum pad 213 at the opening.
To prevent such problems, the technique disclosed in the above-described publication may be modified such that aluminum is formed within both the openings 209 and 216 that are respectively formed in the inter layer insulation film 208 and the insulating protection film 215 positioned thereon, thereby forming an aluminum pad. However, since a total thickness of the inter layer insulation film 208 and the insulating protection film 215 positioned thereon is large, the aluminum pad 213 is forcibly formed into an extremely thick film while making process time necessary for depositing aluminum into the openings 209, 216 extremely long, unfavorably increasing manufacturing cost. The technique may also be modified such that aluminum is formed only within the opening 209 of the inter layer insulation film 208 to form an aluminum pad. However, the aluminum pad 213 formed as described above allows moisture or oxygen to leak through a nonconformal portion formed in the aluminum pad 213 to likely oxidize the copper pad 205 lying directly under the aluminum pad 213, thereby causing the breaking of a part of copper interconnects which include the copper pad 205 as a part thereof and leading to degradation of reliability of a semiconductor device having such construction of bonding pad.
An object of the present invention is to provide a semiconductor device, in which a copper film is interposed between a copper pad and an aluminum pad to reduce a step formed under the aluminum pad to thereby improve reliability of a bonding pad while preventing increase in manufacturing cost of semiconductor device, and further, to offer a method for manufacturing the same.
A semiconductor device according to the present invention comprises a copper pad formed as a part of copper interconnects within a trench formed in an insulation film on a semiconductor substrate, an inter layer insulation film formed to cover the copper pad, a connection copper via metal formed within a connection via hole formed in the inter layer insulation film on the copper pad, an aluminum pad formed on the connection copper via metal and an insulating protection film formed to cover the aluminum pad and having an opening for bonding on the aluminum pad. The semiconductor device may further be constructed such that aluminum interconnects formed from the same layer as the aluminum pad and a connection copper via metal for interconnect formation formed from the same layer as the connection copper via metal, in which the copper interconnects and the aluminum interconnects are electrically connected to each other through the connection copper via metal for interconnect formation.
A method for manufacturing a semiconductor device according to the present invention comprises the steps of forming copper interconnects while forming a copper pad as a part of said copper interconnects within a trench formed in an insulation film on a semiconductor substrate, forming an inter layer insulation film to cover the copper pad, forming a connection via hole in the inter layer insulation film on the copper pad to expose the copper pad, forming a connection copper via metal by filling the connection via hole with copper, forming an aluminum pad on the connection copper via metal, forming an insulating protection film to cover the aluminum pad and forming an opening for bonding in the insulating protection film on the aluminum pad to expose the aluminum pad.
The semiconductor device constructed in accordance with the present invention is manufactured such that a connection via hole is formed in an inter layer insulation film that covers a copper pad, a connection copper via metal is formed within the connection via hole and an aluminum pad is formed on the connection copper via metal. Accordingly, a step formed under the aluminum pad is made substantially equal to zero with the aid of the connection copper via metal and at the same time, a film thickness of the aluminum pad is reduced, thereby reducing manufacturing cost of the semiconductor device. Moreover, even when the connection copper via metal directly lying under the aluminum pad is oxidized, oxidation of the connection copper via metal never affects the copper pad located under the connection copper via metal, thereby advantageously preventing the breaking of the copper interconnects connected to the copper pad.